Secretion of significant amounts of 17 Beta estradiol by human testes was recently demonstrated. The objectives of the proposed research are to clarify the factors which regulate estrogen production by mammlian testes by determining: 1) the in vitro effects of purified preparations of LH and FSH on estrogen and androgen production by intact testes, isolated seminiferous tubules, and isolated interstitium; and 2) the in vivo effects of purified FSH and LH on testicular steroid production in normal men. Intact, decapsulated rat and portions of human testes, isolated seminiferous tubules (rat and human) and isolated interstitium (rat only) will be incubated with and without the addition of tropic hormones. The concentrations of testosterone, 17 Beta estradiol and estrone in the incubation media and testicular tissue will be determined by specific radioimmunoassays. Further, testicular minces and isolated seminiferous tubules will be incubated with tritiated C19 and C21 steroid precursors to determine the intra-testicular site(s) and extent of aromatization. The in vivo effects of purified gonadotropins will be assessed by treating normal adult male volunteers with either FSH or LH. The secretory pattern of FSH and LH and the concentrations of testosterone, 17 Beta estradiol, estrone, progesterone, and 17OH progesterone will be determined before, during, and immediately after treatment. In addition, the concentrations of these steroids in spermatic venous plasma from normal and FSH-treated renal transplant donors will also be determined. These studies should increase our understanding of the interrelationships of the interstitial cells and tubules in androgen and estrogen production, the relative effects of FSH and LH on estrogen production, and perhaps, the complexities of gonadotropin regulation in the human male.